Your project is looking good, although I never flipped one on its side like that before. Should have, we used a lift although after weeks of work standing under there looking up your neck goes off.
Make sure the second coat in the closed compartments is real good (I did three), otherwise good chance it will just start rusting from the inside out all over again like everone of these coupes did starting 40-years ago>>
Even after final coating best to check inside with a borescope through the holes where you removed the plastic caps. Here is one for $79 right now after what you have already done don’t short-cut your work, check, check and check again don’t allow the rust cancer to come back >>>
http://www.harborfreight.com/digital-inspection-camera-67979.html .
Especially after replacing body parts and spot welding new ones in place.
Check everything, the sup-frame member inside and inside the rocker panels “most important”.
Here is a few more.
Roof post inside especially if it has a sunroof.
Behind the rear seat
Inside the truck lid
Inside the hood
Doors seams.
And more……..
About the zinc, at work we have old boxes of zinc-plated bolts that are rusted solid in 5-6 years. The OEM bolts on this coupes were cadmium plated and they were rusting in 2-3 years.
Also about as you call it “lead loading”, got to finish the job right its pretty simple if you have not done it before, get out the flux and wooden paddles and go at it. And about the Bondo, as we say in California no Tijuana body coating please.
And I know what you mean about the color every Mercedes-Benz I ever bought over the years had to be emerald green due to my wife, although they did look very good with tan leather.
Keep us informed and its going to take time although the end-result is the name of the game. And here its a solid structure and a body that can last another 50 years…..